Plasmapheresis for plasma exchange and extracorporeal immunosorption therapy has recently drawn increased interest for clinical application to autoimmune and neoplastic diseases. However, no systematic study to understand the reactions occurring during immunosorption treatment of plasma has been undertaken. A better understanding of the phenomena must be attained if this technique is to be advanced in application to immune complex-\and antibody-mediated diseases. The objective of our research is to obtain a quantitative and fundamental physicochemical understanding of the interactions of immune complexes with immunosorbents. The results will provide a rational basis for the bioengineering design of immunosorbent therapy systems. Our aims are to: (1)\understand the complex interactions in solution involving antigen, antibody, complement and other plasma-borne molecules; (2)\define the reactions in solution between immune complexes and various receptor molecules which bind immunoglobulins, immune complexes or complement components; and (3)\investigate the reactions occurring during immunosorption of immune complexes with a variety of receptor molecules (e.g., protein A, bovine conglutinin and human Clq) bound to solid supports. Experiments will be carried out with model immune complexes prepared from purified monoclonal antibodies and chemically defined antigens and with immune complexes isolated from sera, plasma and effusion fluids of cancer patients. Immune complexes will be characterized by immune complex and physicochemical measurements, and tumor-specific antibody activity will be assayed before and after contacting pathogenic immune complexes with immunosorbents. A new technique, quasi-elastic light scattering, will be used to measure mean size and size distribution parameters of immune complexes in situ in solution and to examine immune complex dissociation and re-equilibration phenomena after contacting with immunosorbents.